The invention relates to an electric tool which is driven by an electric motor 1.
Electric tools of this type are known.
In the known electric tools of the generic type, the variable-speed drive is realised as a rule by via a collector motor whose drive voltage is set in a fashion guided either by speed or by value prescription, and is thus adjusted to a desired speed.
The current is fed to the collector of the collector motor via carbon brushes, with the result that both the collector and the carbon brushes are subjected in practice to substantial wear and, because of the unavoidable considerable heating of the collector under the flow of current between the brushes and the collector, the rotor winding is at risk of failure through overheating and vibrational damage, and constitutes the thermally most critical component in the known electric tools.
It is known that, by contrast with collector motors, three-phase ac motors (asynchronous or synchronous motors), magnetic motors and reluctance motors are considerably lower in wear, and that their thermal loading is substantially easier to manage in operation than that of collector motors. Hitherto, the use of three-phase ac motors in electric tools of the aforementioned type has so far been out of the question, because three-phase current is frequently not present at the place of use, or at least is not available at the required voltage and/or frequency (for example 250 V/200 Hz; 42 V/200 Hz).